DEPOSITION OF COLLAGEN-VI IN THE EXTRACELLULAR-MATRIX DURING MOUSE EMBRYOGENESIS CORRELATES WITH EXPRESSION OF THE ALPHA-3(VI) SUBUNIT GENE

Collagen VI is a microfibrillar component of the extracellular matrix that is predicted to have an important structural role in matrix organ ization and a biological function in mediating cell-matrix interaction s. Secreted collagen VI molecules are composed of three distinct subun its, the alpha 1(VI), alpha 2(VI), and alpha 3(VI) chains. To determin e when, and in which tissues, collagen VI is likely to have a role in embryonic processes, we have analyzed the expression patterns of the t hree subunit chains during postimplantation mouse development by rever se transcriptase-PCR (RT-PCR), in situ hybridization, and immunofluore scence. No collagen VI protein could be detected in the mouse embryo u ntil Day 11.5 of gestation, when low levels were localized within the mesoderm layer of the visceral yolk sac, the subepidermal matrix of br anchial arches, and the vessel wall of the dorsal aorta. Levels of col lagen VI mRNA and protein increased during the period from Days 12.5 t o 14.5 in the visceral yolk sac, subepidermal mesenchyme, lung, gut, m eninges, muscle, perichondrium, and vertebral column. The cartilage ma trix of ribs and developing long bones was not stained with collagen V I antisera, but pericellular staining of chondrocytes was seen in both tissues. Low levels of collagen VI mRNA and protein were seen in the fetal liver except for the connective tissue of the liver capsule, whi ch was highly stained. Collagen VI was first detected at significant l evels in the developing heart on Day 14.5. These data demonstrate a ti ssue-specific onset of collagen VI synthesis and deposition in the ext racellular matrix of developing mouse embryos at a much later stage of development than that reported for fibronectin or collagen I. Sensiti ve RT-PCR assays showed that alpha 1(VI) and alpha 2(VI) mRNAs were am plified from extracts of embryonic tissues as early as Day 7.5, while alpha 3(VI) mRNA was not detected until Day 10.5. Expression of the al pha 3(VI) gene immediately preceded the appearance of collagen VI prot ein in embryonic tissues. This correlation is consistent with the prop osal that expression of alpha 3(VI) chains regulates the formation and secretion of collagen VI trimers and collagen VI matrix deposition du ring development. (C) 1996 Academic Press, Inc.